In the production of titanium dioxide by the sulfate process, so-called dilute acid occurs. Dilute acid consists essentially of dilute sulfuric acid which contains the dissolved salts (mainly iron salts). In the industrial recovery of the dilute acid, the latter is concentrated and filter salts, or green salts, are produced, which are separated. The filter salts are thus produced in large amounts and, on account of their accompanying components they cannot easily be used industrially, but have to be disposed of, often at great expense.
The invention is addressed to the problem of overcoming the disadvantages of the state of the art and especially to create a process whereby iron hydroxide or iron oxide with a content of >90 wt.-% of Fe2O3 can be recovered from the filter salts of dilute acid recovery.